1. Field of Invention
This invention relates generally to optical isolators, and in particular to an isolator in which a light emitter unit and a light detector unit are joined to opposite ends of a dielectric coupler having fiber optic characteristics whereby light from the emitter is propagated by multiple internal reflections to the detector.
2. Status of Art
An optical isolator, also known as an optically-coupled isolator or as an opto-isolator is a four terminal electronic circuit element constituted by a light emitter, a light detector and a dielectric medium therebetween that is transmissive of the optical wavelengths of the emitted light. All these components are in an integrated package, the arrangement being such that the only optical emission impinging on the detector is that emanating from the emitter.
In an optical isolator, an input electric signal is converted by the emitter into a corresponding light signal, and this light signal is intercepted by the detector to be converted into a corresponding output signal. An optical isolator is commonly used between two circuits of a system having a large voltage difference therebetween when it becomes necessary to convey a small signal between the two circuits without changing the basic voltage level of either circuit.
The light emitter in an optical isolator is usually a light emitting diode (LED) formed of gallium arsenide which emits in the infrared or near infrared region of the spectrums. The light detector isolator is usually a photodiode or phototransistor.
In fabricating a conventional otical isolator, the output port of the emitter must be disposed in axial alignment with the input port of the detector, the emitter and the detector being housed in a single hermetically-sealed package or in separate hermetic housings within a common package of non-hermetic design. The fabrication of conventional isolators is made difficult by the need to exactly align the emitter and detector; for should they be misaligned, the isolator will be inoperative.